There may be trouble ahead for the Maid of Might. Supergirl saved the world but lost the man she loved in season two's finale, and when the series returns, we'll see a broken-hearted Kara abandon her civilian life altogether.

Surrounding her at this difficult time will be old friends, new foes and old friends who might become new foes.

Here's a spoiler-filled guide to what happens next, courtesy of Melissa Benoist and the cast, plus new Supergirl showrunners Robert Rovner and Jessica Queller.

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1. Reign of Terror

Flashbacks to Krypton's final days revealed that one more infant was sent to Earth, to "reign" over all humanity – and while "world killer" Reign (Odette Annable) will be this season's Big Bad, she's also going to be "a character unlike any other villain" in the DC TV universe.

"We're going to be very invested in her," says Queller. "It's going to be an emotional, very special arc."

"She's not out to kill everybody, that's not her motive," Annable adds. "She doesn't want to rule the Earth. She has a very specific agenda and her story is powerful, scary and really heartbreaking."

But that doesn't mean that Reign is a soft touch. Far from it. "She's going to be a match for Supergirl!" promises Annable, while Melissa Benoist confirms that "she matches Kara in everything, in powers, in strength".

"It'll almost be like Supergirl fighting herself. It'll be interesting. I'm worried for Kara!"

2. Lena Luthor is a ticking time-bomb

Promoted to series regular status, Katie McGrath will play "a huge role" this season as Lena Luthor, who we're told will have "a surprising connection to Reign".

Lena has so far proved herself a valuable ally to Supergirl, even if her connection to the Luthor family means that some of Kara's allies will never trust her completely. But are they right to be suspicious?

"She's a ticking time-bomb," confirms Keller, while Rovner adds: "It's an interesting journey to be able to take her on. Will that one very bad day, or one very bad choice, tip her over the edge?"

"The best characters are those that are flawed," McGrath herself suggests. "Do I hope that one day Lena becomes evil? I hope that she has the potential. You want to be constantly surprised."

3. Cat Grant will be back – and it'll be amazing

Having stepped away from Supergirl as a series regular last year, Calista Flockhart will continue to recur in the third season, with an appearance in the premiere already confirmed.

"Calista's in the first episode this season and the way that they integrated her in is so brilliantly clever," Benoist enthuses. "I can't wait for people to see it. First of all, it's hilarious, also it's very relevant to what the country's going through right now!"

4. The Legion of Superheroes are – probably – coming

Last we saw Mon-El (Chris Wood), he'd been forced to leave Earth for good after the planet became hostile to his species. Alone in space, his pod was sucked into a wormhole... with fans speculating he might've ended up in the Phantom Zone.

In the original DC comics, he was eventually recovered by the Legion of Superheroes... so could Supergirl follow that path?

"If and when we do see Mon-El again... there's very little I can tease, but what I do know about it, I'm very excited about," said Wood, with the world's worst poker face. "I think it's going to add a whole new dimension to the show and something that I think will make fans very happy to see."

Quizzed directly on the possibility of the Legion making an appearance, he added: "I think anything's possible in DC right now. They've had such success in the TV space and every character they've tried, even those that people thought might be too big for TV... it's paid off in a big way, so I don't think that would be a bad idea!"

5. The fate of Jeremiah Danvers will be revealed

Jeremiah (Dean Cain) betrayed Alex (Chyler Leigh) and the entire DEO when he stole the list of all registered aliens and handed it over to Cadmus – but it was all part of a misguided effort to protect his family.

He remains in Cadmus's clutches and while the fate of the character "remains a mystery" as we enter this season, Jeremiah "will come into play at some point".

"Dean and Helen [Slater, who plays Eliza Danvers] are still part of our world," Rovner said. "We love having the legacy actors back when there's a chance that we can do that."

6. Miss Martian will be back... at some stage

With actress Sharon Leal – who appeared in 7 episodes of season two as M'Gann – having landed a full-time gig elsewhere, Supergirl will have to work around her schedule this year.

"It's the same with Snapper (Ian Gomez) and some of the other recurring cast," Harewood explained. "It very much depends on their availability. We love them and we would love to see them back, but it depends."

7. Don't expect a whole lot of Cyborg Superman

Harewood of course plays a dual role on Supergirl – J'onn, who's assumed the form of Hank Henshaw, and the real Henshaw, who's been transformed into the deranged Cyborg Superman.

But he's gone on record as saying he didn't much enjoy playing the latter part. "I did mention to one of the writers at the end of the second season that [Cyborg Superman] didn't really go anywhere, so it was a little frustrating.

"I think they understand that. J'onn's such an interesting character to play that I just felt there were a few holes with that [Henshaw] character and I don't think we quite sewed them up. So I'm looking forward to more J'onn and maybe less Cyborg."

8. We might get to see Winn's dark side

Kara's best pal Winn Schott is always quick with the quips, but Jeremy Jordan thinks the character's sunny persona is masking a lot of pain.

"The thing that I love so much about Winn is his sense of humour, but it's covering up deeper things," Jordan said. "He's got some demons that he has pushed down for a long time."

But not, perhaps, for much longer, with this season of Supergirl set to explore some of Winn's "family issues" – let's not forget that his father was the villainous Toyman...

"We're gonna explore some of his past a little bit more this season, which I'm really excited about. We might try to figure out where his lineage comes from and maybe explore a little bit more of the dark side to Winn."

9. Winn's feelings for Kara could bubble up again

Winn was secretly smitten with Kara for the longest time and while both appeared to have moved on, Jordan suggests that his feelings could resurface this year and cause a few problems.

"He was in love with Kara for 2 or 3 years, before he finally said something and was immediately rejected, and then is forced to hang out with her every day. He still likes her, they're still friends, but there's a disconnect between them that hasn't been fully hashed out.

"I think he's buried a lot, so I'd love to see some of that get unearthed this season. I think we'll start to do that."

10. It's a "darker" season - but it's about "humanity"

"This season's going to be a little darker, given the cliffhangers of last season," Rovner confirmed. "Thematically, it's going to be about humanity, and each character's going to be dealing with their emotions, their human feelings, [while] also being a superhero or an alien."

"This season's very much about being human, and find the humanity even in these alien characters," David Harewood echoes. "J'onn's story arc may be about him finding himself.

"Has he strayed too far from Mars? Does he need to go back to Mars? Or will he remain on planet Earth? It's going to be quite emotional, I think."

Supergirl will return to The CW on Monday, October 9 at 8/7c. The series airs on Sky1 in the UK.